1. Field of the Invention
The present invention relates to transmission channel allocation methods and radio apparatuses using the same. More particularly, the present invention relates to a transmission channel allocation method and a radio apparatus using the same for allocating a channel to be used for transmission to a user requesting connection in a PDMA (Path Division Multiple Access) communication system where a plurality of users transmit and receive data such as audio and video using channels of the same frequency and the same time.
2. Description of the Background Art
In a conventional portable telephone system such as PHS (Personal Handy phone System), when a plurality of users request connection to a base station, determination is made as to whether a user is connected in accordance with a desired wave level of a radio wave from the requesting user and an undesired wave level of a radio wave of the other user.
FIGS. 13 and 14 are schematic diagrams shown in conjunction with a channel allocation method of a conventional portable telephone system.
FIG. 13 relates to the case where the undesired wave level is too high to enable connection of the newly requesting user (hereinafter referred to as a newly requesting user) in the conventional portable telephone system.
First, for example, at a base station CS1, undesired wave levels (hereinafter referred to as U wave levels) to a slot which is not connected (not allocated to a user) at all frequencies are measured in advance. Then, a table showing a relationship between each of the frequencies and the U wave level is produced.
If a user PS2 newly requests connection, base station CS1 measures a desired wave level (hereinafter referred to as a D wave level) of user PS2. If a ratio of D wave level to the U wave level (hereinafter referred to as a D/U ratio) is equal to or smaller than a prescribed value at a given frequency (f1 in FIG. 13), that frequency cannot be used for communication with user PS2.
On the other hand, FIG. 14 relates to the case where the U wave level is low enough to allow connection of the newly requesting user in the conventional portable telephone system. If the D/U ratio in the above mentioned table is at least the prescribed value, base station CS1 uses the frequency for communication with newly requesting user PS2.
The above described communication channel allocation method suffers from the problem that communication cannot be established with the base station through a channel if the other user is in communication with another base station which is located near the present base station.
Recently, in the field of the mobile communication systems, various transmission channel allocation methods have been proposed to effectively use the frequencies. Some of the methods are actually in practice.
FIG. 15 is a diagram showing arrangements of channels in various communication systems of Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and PDMA.
Referring first to FIG. 15, the systems of FDMA, TDMA, and PDMA will be briefly described. FIG. 15(a) relates to the FDMA system, where analog signals of users 1-4 are frequency-divided to be transmitted in radio waves of different frequencies f1-f4. The signals of users 1-4 are separated by frequency filters.
In the TDMA system shown in FIG. 15(b), the digitized signals of respective users are time-divided and transmitted in radio waves of different frequencies f1-f4 at every constant period of time (time slot). The signals of respective users are separated by frequency filters and by time synchronization between a base station and a mobile terminal device of each user.
Recently, the PDMA system has been proposed to improve the radio wave frequency usability to comply with the proliferation of portable telephones. In the PDMA system shown in FIG. 15(c), one time slot of the same frequency is spatially divided to transmit data of a plurality of users. In this system, signals of respective users are separated by frequency filters, time synchronization between a base station and a mobile terminal device of each user, and interference canceller such as adaptive arrays.
FIG. 16 is a schematic block diagram showing a transmission/reception system 2000 of a conventional base station for PDMA.
In the structure shown in FIG. 16, four antennas #1 to #4 are provided to distinguish between users PS 1 and PS 2.
In a reception operation, outputs of respective antennas are applied to RF circuit 101, where they are amplified by a reception amplifier and subjected to frequency conversion by local oscillation signals. Thereafter, any unwanted frequency signal is eliminated by a filter. Further, the signals are subjected to A/D conversion to be applied to a digital signal processor 102 as digital signals.
Digital signal processor 102 includes a channel allocation standard calculator 103, a channel allocation apparatus 104, and an adaptive array 100. Channel allocation standard calculator 103 preliminary calculates to determine if the signals from two users can be separated by the adaptive array. Based on the calculation result, channel allocation apparatus 104 provides to adaptive array 100 channel allocation information including user information for selection of the frequency and time. Adaptive array 100 separates the signal of a particular user by performing in real time a weighting operation on signals from four antennas #1 to #4 in accordance with the channel allocation information.
[Structure of Adaptive Array Antenna]
FIG. 17 is a block diagram showing a structure of a transmitting/receiving portion 100a corresponding to one user in adaptive array 100. Referring to FIG. 17, n input ports 20-1 to 20-n are arranged for extracting the signal of an intended user from input signals including a plurality of user signals.
The signals input to respective input ports 20-1 to 20-n are applied to a weight vector controlling portion 11 and multipliers 12-1 to 12-n through switch circuits 1-1 to 10-n.
Weight vector controlling portion 11 calculates to obtain weight vectors w1i-wni using the input signals, a training signal corresponding to a particular user signal which has preliminary been stored in a memory 14, and an output from an adder 13. Here, a subscript i indicates that the weight vector is used for transmission/reception with respect to the ith user.
Multipliers 12-1 to 12-n respectively multiply the input signals from input ports 20-1 to 20-n and weight vectors w1i-wni for application to adder 13. Adder 13 adds output signals from multipliers 12-1 to 12-n for output as a reception signal SRX (t), which is also applied to weight vector controlling portion 11.
Further, transmitting/receiving portion 100a includes multipliers 15-1 to 15-n receiving an output signal RTX (t) from the adaptive array of the radio base station and multiplying it by each of w1i-wni that have been applied from weight vector controlling portion 11 for output. Outputs form multipliers 15-1 to 15-n are applied to switch circuits 10-1 to 10-n. In other words, switch circuits 10-1 to 10-n provide signals applied from input ports 20-1 to 20-n to a signal receiving portion 1R for signal reception, and provide signals from a signal transmitting portion IT to input/output ports 20-1 to 20-n for signal transmission.
[Operation Principle of Adaptive Array]
Now, the operation principle of transmitting/receiving portion 100a shown in FIG. 17 will be briefly described.
In the following, for simplification of the description, assume that four antenna elements are provided and two users PS are in connection at the same moment. Then, signals applied from respective antennas to receiving portion 1R are represented by the following equations.
RX1(t)=h11Srx1(t)+h12Srx2(t)+n1(t) xe2x80x83xe2x80x83(1) 
RX2(t)=h21Srx1(t)+h22Srx2(t)+n2(t) xe2x80x83xe2x80x83(2) 
RX3(t)=h31Srx1(t)+h32Srx2(t)+n3(t) xe2x80x83xe2x80x83(3) 
RX4(t)=h41Srx1(t)+h42Srx2(t)+n4(t) xe2x80x83xe2x80x83(4) 
Here, a signal RXj (t) is a reception signal of the jth (j=1, 2, 3, 4) antenna, whereas signal Srxi (t) is transmitted from the ith (i=1, 2) user.
Further, a coefficient hji represents a complex coefficient of the signal from the ith user received by the jth antenna, whereas nj (t) represents a noise included in the jth reception signal.
The above equations (1) to (4) can be placed into vector formats as follows.
X(t)=H1Srx1(t)+H2Srx2(t)+N(t) xe2x80x83xe2x80x83(5) 
X(t)=[RX1(t), RX2(t), . . . , RXn(t)]T xe2x80x83xe2x80x83(6) 
Hi=[h1i, h2i, . . . , hni]T, (i=1, 2) xe2x80x83xe2x80x83(7) 
N(t)=[n1(t), n2(t), . . . , nn(t)]T xe2x80x83xe2x80x83(8) 
It is noted that [ . . . ]T is the transposition of [ . . . ] in the equations (6) to (8).
Here, X (t) is an input signal vector, Hi is a reception signal coefficient vector of the ith user, and N (t) is a noise vector.
With reference to FIG. 15, the adaptive array antenna outputs, as reception signal SRX (t), the signal obtained by multiplying input signals of respective antennas by weight coefficients w1i-wni and adding them together. It is noted that there are four antennas in this example.
The operation of the adaptive array in the above described environment, for example when a signal Srx1 (t) transmitted by the first user is extracted, is as follows.
An output signal y1 (t) from adaptive array 100 can be represented by the following equation that is obtained by multiplying input signal vector X (t) by weight vector W1.
y1(t)=X(t)W1T xe2x80x83xe2x80x83(9) 
W1=[w11, w21, w31, w41]T xe2x80x83xe2x80x83(10) 
In other words, weight vector W1 has weight coefficients wj1 (j=1, 2, 3, 4) to be multiplied by jth input signal RXj (t).
By substituting input signal vector X (t) of equation (5) into equation (9), the following equation is obtained.
y1(t)=H1W1TSrx1(t)+H2W1TSrx2(t)+N(t)W1T xe2x80x83xe2x80x83(11) 
Here, if adaptive array 100 operates favorably, weight vector W1 is sequentially controlled by weight vector controlling portion 11 to satisfy the following simultaneous equation in accordance with a well-known method.
H1W1T=1 xe2x80x83xe2x80x83(12) 
H2W1T=0 xe2x80x83xe2x80x83(13) 
When weight vector W1 is perfectly controlled to satisfy the above equations (12) and (13), output signal y1 (t) from adaptive array 100 will eventually be represented by the following equation.
y1(t)=Srx1(t)+N1(t) xe2x80x83xe2x80x83(14) 
N1(t)=n1(t)w11+n2(t)w21+n3(t)w31+n4(t)w41 xe2x80x83xe2x80x83(15) 
More specifically, signal Srx1 (t) that has been transmitted by the first of the two users is obtained for output signal y1 (t).
On the other hand, referring to FIG. 15, input signals STX (t) to adaptive array 100 is applied to transmitting portion 1T of adaptive array 100 and applied to one inputs of multipliers 15-1 to 15-n. The other inputs of the multipliers are supplied with copies of weight vectors w1i-wni, which have been obtained by calculation in accordance with reception signals by weight vector controlling portion 11 as described above.
The input signals that have been weighted by the multipliers are transmitted to corresponding antennas #1 to #n through corresponding switches 10-1 to 10-n to be further transmitted.
Here, users PS1 and PS2 are distinguished as follows. Namely, radio signals from portable telephones are transmitted in frame configurations. The radio signal from the portable telephone mainly includes a preamble of a signal sequence known to the radio base station, and data (such as audio) of a signal sequence unknown to the radio base station.
The signal sequence of the preamble includes a signal column of information for determining if the user is desirable for the radio base station to communicate. Weight vector controlling portion 11 of adaptive array of radio base station 1 compares a training signal corresponding to user A that is obtained from memory 14 and the received signal sequence for performing weight vector control (determination of weighting coefficient) to extract a signal which is likely to include the signal sequence corresponding to user PS1.
Recently, due to the rapid proliferation of portable telephones, the usability of channels is now approaching its limit. In the future, it is expected that allocation requests from users would exceed the number of available transmission channels. To meet the situation, channel allocation must be performed while effectively utilizing empty channels in the above described mobile communication system for PDMA.
In the above described PDMA system, one time slot of the same frequency is spatially divided to transmit data of a plurality of users. Thus, a transmission channel must be allocated to each user such that interference among signals is eliminated by time synchronization between the base station and a mobile terminal device of each user. Then, it becomes difficult to maintain a sufficient communication quality unless allocation is performed to sufficiently reduce the interference among the plurality of users.
An object of the present invention is to provide a transmission channel allocation method capable of efficiently allocating a transmission channel to a user who is requesting connection (hereinafter referred to as a newly requesting user) while reducing interference between signals, and to a radio apparatus using the same.
In short, the present invention is a method of allocating transmission channels to respective terminal devices for multiple connection to a base station having array antennas in response to connection requests from a plurality of terminal devices, including a step of measuring a reception signal coefficient vector of an undesired wave (a U wave) for a preliminary multiplexed slot and producing a table of U wave levels, and a step of allocating a transmission channel from empty transmission channels to a newly requesting user in accordance with a magnitude of cross correlation of a reception signal of the undesired wave and a reception signal of the newly requesting user.
According to another aspect, the present invention is a method of allocating transmission channels to respective terminal devices for multiple connection to a base station having array antennas in response to connection requests from a plurality of terminal devices, including a step of measuring a reception signal coefficient vector and a U wave level for a preliminary multiplexed slot and generating a table of the U wave levels, and a step of allocating a transmission channel from empty transmission channels to a newly requesting user in accordance with a magnitude of cross correlation of a reception signal of the U wave and a reception signal from the newly requesting user as well as a ratio of the U wave level and a reception signal level of the newly requesting user.
According to still another aspect, the present invention is a radio apparatus for performing path-divided multiple connection with respect to a plurality of terminal devices, including array antennas, a plurality of reception signal separating portions, a reception signal coefficient vector calculating portion, a storing portion, and a channel allocating portion.
The plurality of reception signal separating portions separate reception signals in real time by multiplying reception weight vectors of terminal devices by reception signals from the array antennas.
The reception signal coefficient vector calculating portion measures reception signal coefficient vectors of a U wave and reception waves from respective terminal devices for a multiplexed slot.
The storing portion stores a table of the reception signal coefficient vectors of the U wave.
The channel allocating portion allocates a transmission channel from empty transmission channels to a newly requesting user in accordance with a magnitude of cross correlation of the reception signal coefficient vector of the U wave and the reception signal coefficient vector of the newly requesting user.
According to still another aspect, the present invention is a radio apparatus for performing path-divided multiple connection with respect to a plurality of terminal devices including array antennas, a plurality of reception signal separating portions, a reception signal coefficient vector calculating portion, a storing portion, and a channel allocating portion.
The plurality of reception signal separating portions separate reception signals in real time by multiplying reception weight vectors for respective terminal devices by reception signals from the array antennas.
The reception signal coefficient vector calculating portion measures a U wave and reception signal coefficient vectors of a U wave and reception waves from respective terminal devices for a multiplexed slot.
The reception signal power calculating portion derives reception signal power of each terminal device and reception signal power of the U wave.
The storing portion stores a table of the reception signal coefficient vector of the U wave and a table of the reception signal power of the U wave.
The channel allocating portion allocates a transmission channel from empty transmission channels to a newly requesting user in accordance with a magnitude of cross correlation of the reception signal coefficient vector of the U wave and the reception signal coefficient vector of the newly requesting user as well as a ratio of a U wave power level and the reception signal power level of the newly requesting user.
Therefore, a main advantage of the present invention is that the channel is allocated to the newly requesting user for which path multiplex connection is attained without difficulty in terms of a base station, so that the transmission channel can be allocated to the newly requesting user even when the U wave level per se is high. Therefore, a transmission channel allocation method capable of improving transmission channel usability is provided.
Another advantage of the present invention is that a radio apparatus is provided which is capable of allocating a transmission channel to a newly requesting user and improving transmission channel usability even when the U wave level is high since the channel is allocated to a newly requesting user for which path multiplex connection is attained without difficulty in terms of the base station.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.